From 1990 to 2017, the PGHM carried out 347 rescue operations in the Goûter couloir, which resulted in 102 deaths and 230 injuries; On average, 3.7 fatal accidents per summer season, representing the highest frequency in the Alps.
Rock destabilization is responsible for 29% of the accidents that took place in the Couloir du Goûter.
Thus, Jacques Mourey, a researcher in geography, conducted a study on rock destabilization in the Goûter couloir. The results show when and why rockfalls occur. Moreover, the study offers valuable information for anyone who wants to climb the Mont-Blanc summit.
The "Corridor of Death"
Also known as the "Death Gully", the infamous Grand Couloir is a couloir on the Aiguille du Goûter, located at 3,340 m (10,958 ft) altitude.
This couloir is found on the Goûter Route, one of the two normal mountaineering routes used to reach the Mont-Blanc summit, and the most popular one.
Crossing the Grand Couloir is very dangerous, mainly because of falling rocks and ice. Rock destabilization is the direct cause of nearly 30% of accidents that happened here in the past three decades. Other accidents were indirectly caused by rock destabilization, as climbers tend to look up the Couloir, hoping to see and avoid any falling rocks. By averting their attention from the narrow and dangerous path, the risk of slipping increases dramatically.
A study funded by Petzl foundation
The first study on rock destabilisation in the Grand Couloir du Goûter conducted by Petzl Foundation took place in the summer of 2011.
Needing to collect more precise data over a longer period of time, a new study was carried out over the summers of 2018 and 2019.
The purpose of these studies was to determine when rockfalls are more frequent, and what causes them.
The results of the two studies are very similar and show certain patterns.
Three seismic sensors were placed on one side of the corridor in 2018, and two more were added on the other side the following year. These sensors are capable of detecting falls of a volume of just over 100 kg.
By correlating these results with snow levels, soil temperature and rainfall, the scientific team was able to determine very precisely when rockfalls are most frequent and why.
Key Insights of Study
The Petzl study revealed some clear trends. "The largest events occurred during or following liquid precipitation. During these periods, the volume of rock destabilised was generally greater than average", reveals the study. Therefore, mountaineers need to be particularly cautious during periods of snowmelt or after rain/storms.
The frequency of rock destabilisation events was lower in the second half of the summer season, but the longest events (“boulder showers”) and those involving the highest volumes of material also occurred during this period.
The presence of snow in the couloir is not necessarily a guarantee of safety since snowmelt promotes rock destabilisation
Rock destabilisation events grew more frequent and larger in size when the couloir became exposed to the sun.
The highest frequency of rock destabilisation events was recorded between 6 pm and 8 pm. The least frequency was recorded between 9 am and 10 am. However, the couloir was as dangerous at 3 pm as it was at 10 pm.
In 2019, 2,662 events were recorded over a period of 68 days, an average of 39 events per day.
In 2019, a rock destabilisation event was recorded every 37 minutes on average. During the peak activity between 7 pm and 8 pm, rockfalls took place every 24 minutes on average.
The study can be found here.
Sources @ Petlz Foundation, Le Dauphine, Radio Mont Blanc
